1. Field of the Invention
The present invention relates to novel fluoran derivatives. More particularly, it relates to a heat sensitive record sheet having a coated layer comprising a novel fluoran derivative which imparts color-development in black color as a color precursor.
2. Description of the Prior Art
Certain fluoran compounds have been disclosed in U.S. Pat. No. 3,746,562, U.S. Pat. No. 3,920,510 and Japanese Examined Patent Publication No. 23204/1976. When these fluoran compounds are used as color precursors for heat sensitive record sheet, there are disadvantages of the ground color density, the coloring initiation temperature and the rising for coloring. It is not possible to impart satisfactory effect for coloring in black on a heat sensistive record sheet. For example, 2-anilino-3-methyl-6-diethylaminofluoran disclosed in U.S. Pat. No. 3,746,562 partially colored in a preparation of the heat sensitive record paper to cause high ground color density of the heat sensitive record paper and a rising for coloring of the record paper is disadvantageously low. When 2-anilino-3-methyl-6-N-methyl-N-cyclohexylaminofluoran is used as disclosed in Japanese Examined Patent Publication No. 23204/1976, the rising for coloring of the heat sensitive record sheet is not satisfactory. On the other hand, when 2-(2-chlorophenyl)amino-6-diethylaminofluoran is used as disclosed in U.S. Pat. No. 3,920,510, the coloring initiation temperature is disadvantageously high though the ground color density is low and the rising for coloring is not satisfactory.
The rising for coloring means a rising of a curve in a diagram of color density-coloring temperature curve given by plotting color densities on the ordinate and coloring temperature on the abscissas as a value given by multiplying 100 to tan .theta. in the maximum slant of the curve.